This application is based on and claims the benefit of German Patent Application No. 198 44 869.4. filed on Sep. 30, 1998.
The invention relates to a contact element for connecting a ribbon cable with circular conductors, whereby the contact element comprises a plurality of mutually insulated parallel conductor strips made of a conductive material, to the one end of which a circular conductor may be attached and the other end of which is provided with a surface to which a strand of the flat ribbon cable may be fixed through a material connection, as well as a rotary connector with such a contact element.
Interference-free power or signal transmission between parts of a device that are rotatable with respect to each other within a limited angular range is a problem frequently encountered. For example, a permanently secure power supply for triggering the airbag in the steering wheel of a motor vehicle is of decisive importance. Since sliding contacts, due to wear and fluctuating contact resistances, are unsuitable for this purpose, rotary connectors with ribbon cables have been developed to ensure a reliable connection.
The ribbon cable (hereinafter referred to as FBL) is disposed in the gap between two mutually rotatable housing parts of the rotary connector and fixed to both housing parts by its end faces. Preferred is a flat ribbon cable made of one or a plurality of flexible metal strips spaced at a distance from each other and embedded between two plastic strips. In the simplest case, the FBL extends helically like a clock spring within the gap. When the housing parts are rotated relative to each other, the diameter and the number of the turns changes as a function of the direction of rotation. Alternatively, the turns of the FBL extend along the radially inner and outer wall of the gap with opposite sense of rotation, whereby a reversal point is provided between the two cable sections. In this case, as the housing parts of the connector are rotated relative to each other, the cable is unwound from the one wall and taken up by the other wall. It is also known to dispose guide elements or elastic elements within the gap and to make the FBL from an elastic material to ensure reliable guidance as the housing parts are rotated relative to each other and to prevent damage.
Generally, the rotary connector is externally connected by circular conductors, i.e., wires or flexible leads with an at least approximately circular cross-section. Accordingly, a contact element is required for the electrical connection of the circular conductors and the strands of the ribbon cable. DE 41 19 769 A1 discloses a rotary connector with such a contact element. This contact element comprises several parallel mutually insulated metal strips that are connected to the strands of the FBL, for example by soldering or welding. The opposite ends of the conductor strips are made as plug contacts into which counter contacts connected with the circular conductors may be plugged. The disadvantage, however, is that this construction requires the prefabrication of the circular conductors with corresponding counter contacts, which is not only high in labor, but also requires tools for manufacturing and mounting the counter contacts. Furthermore, it increases the number of connecting points in the course of the cable and thus the risk of faulty contacts, particularly if the contacts are exposed to constant vibrations in a motor vehicle.